Apparatus for transporting webs in photographic copying machines or the like

ABSTRACT

A photographic printing machine with a single pair of advancing rolls which are located upstream or downstream of the gate and pressure plate and are driven intermittently to place a fresh increment of a photosensitive web into register with the window of the gate prior to the making of an exposure. A roller or pad consisting of or including soft rubber or similar friction generating material is located downstream or upstream of the gate opposite a back support and is moved toward the back support away from the advancing rolls in response to movement of the pressure plate to its operative position, or by a discrete actuating means, so as to tension the web between the back support and the advancing rolls not later than when the pressure plate reaches its operative position.

United States Patent [191 Steinberger et al.

[ 51 Sept. 17, 1974 [73] Assignee: AGFA-Gevaert Aktiengesellschaft,

Leverkusen [22] Filed: Jan. 24, 1973 [21] Appl. No.: 326,298

[30] Foreign Application Priority Data Jan. 26, 1972 Germany 2203479[52] US. Cl 226/115, 226/143, 226/151, 226/195, 242/753 [51] Int. ClB6511 23/08 Field of Search 226/117, 36, 49, 50, 147, 226/148,149, 150,151, 195, 115,143,156, 108; 242/753 [56] References Cited UNITED STATESPATENTS 2,948,177 8/1960 Arvidson 83/175 X 3,460,158 8/1969 Bravenel226/195 X Primary Examiner-Richard A. Schacher Attorney, Agent, orFirm-Michael S. Striker [57] ABSTRACT A photographic printing machinewith a single pair of advancing rolls which are located upstream ordownstream of the gate and pressure plate and are driven intermittentlyto place a fresh increment of a photosensitive web into register withthe window of the gate prior to the making of an exposure. A roller orpad consisting of or including soft rubber or similar frictiongenerating material is located downstream or upstream of the gateopposite a back support and is moved toward the back support away fromthe advancing rolls in response to movement of the pressure plate to itsoperative position, or by a discrete actuating means, so as to tensionthe web between the back support and the advancing rolls not later thanwhen the pressure plate reaches its operative position.

17 Claims, 9 Drawing Figures SHEET 2 OF 2 APPARATUS FOR TRANSPORTINGWEBS IN PHOTOGRAPIIIC COPYING MACHINES OR THE LIKE BACKGROUND OF THEINVENTION The present invention relates to apparatus for transportingwebs of paper, photographic film or other flexible material, and moreparticularly to apparatus for stepwise transport of webs in photographicprinting or copying machines or the like. Still more particularly, theinvention relates to improvements in apparatus which can be utilizedwith advantage to place successive portions or increments ofphotosensitive webs into register with the gate of a photographicprinting or copying machine prior to exposure of such increments toprinting light.

It is well known to provide a photographic printing machine with meansfor tensioning the web portion behind the window of the gate prior toexposure of such web portion to printing light. As a rule, the web istensioned between two pairs of advancing rolls which flank the gate ofthe printing machine. The diameters of advancing rolls which are locatedupstream of the gate are smaller than the diameters of the other pair ofadvancing rolls so that, if the angular speed of all advancing rolls isthe same, the peripheral speed of the upstream rolls is less whereby theweb is automatically tensioned and slips relative to the upstream rollswhen the rolls are set in rotary motion. A drawback of such transportingapparatus is that the web is tensioned at all times, i.e., not onlyduring exposure to printing light but also during stepwise transport.Furthermore, the web slips relative to the upstream rolls during eachstepwise transport to cause pronounced wear on the upstream rolls and toprevent accurate transport of the web by steps of identical length. Thematerial which is rubbed off the web, especially off the rear oruncoated side of the web, contaminates the machine and affects thequality of prints. Still further, the diameters of all advancing rollsmust be maintained within a very narrow range of tolerances and the biasof upstream rolls upon the web must be regulated with a high degree ofprecision. All this contributes to initial and maintenance cost of themachine.

SUMMARY OF THE INVENTION An object of the invention is to provide a webtransporting apparatus, particularly for use in a photographic printingor copying machine, wherein the web need not be tensioned with asubstantial force during lengthwise transport.

Another object of the invention is to provide a web transportingapparatus which can operate properly with a single pair of advancingrolls.

A further object of the invention is to provide a web transportingapparatus with novel and improved means for tensioning the web uponcompleted stepwise transport and in such a way that the wear on thetensioning means is less pronounced than in heretofore known apparatus.

An additional object of the invention is to provide a web transportingapparatus wherein the stepwise transport of a web, such as a strip ofpaper one side of which is coated with a layer of photosensitivematerial, and the tensioning of the web upon completion of each stepwisetransport result in generation of negligible quantities of dust.

Still another object of the invention is to provide a web transportingand tensioning apparatus which can automatically compensate fordifferences in the thickness of successive portions of a single weband/or for differences in thicknesses of successive webs.

A further object of the invention is to provide a web transporting andtensioning apparatus wherein the slippage of tensioning means relativeto the web is less pronounced and can be controlled with a higher degreeof accuracy than in conventional apparatus.

An ancillary object of the invention is to provide a photographicprinting or copying machine which embodies the improved web transportingand tensioning apparatus.

The invention is embodied in an apparatus for stepwise transport ofelongated webs, particularly for stepwise transport of photosensitivewebs in photographic copying or printing machines. The apparatuscomprises a single pair of intermittently driven advancing rolls whichserve to transport a web lengthwise along a predetermined path,preferably behind the window in the gate in a photographic printingmachine and in front of a pressure plate which is movable between anoperative position of engagement with the web behind the gate and aninoperative or retracted position, a roller, pad or an analogousfriction generating device which is adjacent to one side of the path andis spaced apart from the advancing rolls so that the gate and thepressure plate are located between the friction generating device andthe advancing rolls, a back support (e.g., a rigid plate-like memberwhich may but need not be integral with the gate) adjacent to the otherside of the path opposite the friction generating device, and displacingmeans which is actuatable (e.g., by a rotary electromagnet) to urge thefriction generating device toward the back support and to simultaneouslymove the friction generating device away from the advancing rollswhereby the friction generating device automatically tensions the webbetween the advancing rolls and the back support. The displacing meansmay include the pressure plate and is preferably actuated shortly beforeor immediately after completion of each intermittent movement of theadvancing rolls so that the web is properly tensioned not later thanwhen its rear side is engaged and clamped by the pressure plate wherebythe web portion which registers with the window of the gate cannotchange its position during exposure of the web to printing light.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved web transporting apparatus itself, however, both as to itsconstruction and its mode of operation, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary diagrammaticpartly elevational and partly vertical sectional view of a photographicprinting machine comprising a web transporting and tensioning apparatuswhich embodies one form of the invention;

FIG. 2 is a fragmentary vertical sectional view of the printing machineand of a slightly modified web transporting and tensioning apparatus;

FIG. 3 is a similar fragmentary sectional view of the printing machineand a web transporting and tensioning apparatus constituting a furthermodification of the apparatus shown in FIG. 1;

FIG. 4 is a fragmentary sectional view of a printing machine and anelevational view of a fourth web transporting and tensioning apparatus;

FIG. 5 is a fragmentary sectional view of a printing machine and of afifth web transporting porting and tensioning apparatus;

FIG. 6 illustrates the electric circuit of the electromagneticdisplacing means in the friction generating device of the apparatusshown in FIG. 5;

FIG. 7 is a view similar to that of FIG. 5 but showing a portion of asixth web transporting and tensioning apparatus;

FIG. 8 is a fragmentary sectional view of a printing machine and of aseventh web transporting and tensioning apparatus; and

FIG. 9 is a diagram of an electric circuit for the apparatus of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a portion ofa photographic copying or printing machine which comprises a lightsource 1 located in front of a reflector 2 and behind a system ofcondenser lenses 3. The lenses 3 are located behind a support (notshown) fora light-transmitting original 4 (e.g., a photographicnegative) which is imaged by an objective lens 5 onto the photosensitivelayer of an elongated web 7. The latter is located behind a gate 6having a rectangular window 6a through which the printing light passesto reach the photosensitive layer of the web 7. A pressure plate 8 ismounted behind the path for the web 7 and is movable by any suitableconventional actuating mechanism (e.g.. an electromagnet) so as to pressthe web 7 against the adjacent surface of the gate 6 during exposure ofphotosensitive material to printing light issuing from the source 1 andpassing through the original 4. The pressure plate 8 is lowered, asviewed in FIG. 1, prior to start of each printing or copying operationand is thereupon returned to the illustrated retracted or inoperativeposition so as to allow for lengthwise movement of the web 7 in adirection to the right, as viewed in FIG. 1, whereby an unexposedincrement or portion of photosensitive material at the underside of theweb moves into register with the window 6a.

A roll of fresh (unexposed) web 7 is stored on a supply reel 10 which isinstalled in the interior of a lighttight cassette or container 9. Theweb 7 passes over fixed guide rollers 11, 12 in the cassette 9,thereupon over a third fixed guide roller 13, over a movably mountedloop forming roller 14, and through the nip of two advancing rolls 15,16 which are located immediately or closely ahead of the gate 6 and atleast one of which is driven intermittently to advance the web 7 instepwise fashion.

The exposed web 7 is collected by the driven takeup reel 21 in a secondcassette or container 22. Prior to reaching the takeup reel 21,successive increments of the web 7 must pass over a spring-biased loopforming roller 17 and three fixed guide rollers 18, 19 and 20.

In addition to the advancing rolls l5, 16, the improved web transportingapparatus comprises a friction generating device here shown as a softrubber pad 23a which is attached to a coupling element in the form of aleaf spring 23. The latter is riveted or otherwise secured to a bracket8a of the pressure plate 8. The curvature of the leaf spring 23 isselected in such a way that the pad 23a tends to move in a direction tothe right, as viewed in FIG. 1, when the pressure plate 8 is caused tomove toward the rear side of that portion of the web 7 which overliesthe gate 6. The gate comprises a rigid plate-like extension 24 which islocated opposite the pad 23a and constitutes a back support for theadjacent portion of the web 7. The parts 8a and 23 constitute or formcomponents of a displacing means which urges the pad 23a toward the backsupport 24 and simultaneously moves the pad 23a away from the advancingrolls 15, 16 in response to movement of the pressure plate 8 to itsoperative position.

The operation:

When the printing machine is idle, the parts assume the positions shownin FIG. 1. It is assumed that the advancing rolls 15, 16 have completeda stepwise transport of the web 7 in the direction indicated by arrow Aso that the window 6a of the gate 6 registers with an unexposed portionof the photosensitive layer at the underside of the web. The web portionbetween the advancing rolls 15, 16 and the fixed guide roller 18 istensioned to a certain extent by the pivotable loop forming roller 17under the action of the spring 17a. In order to insure that the webportion which overlies the window 6a will be located in the focal planeof the objective 5, the aforementioned actuating mechanism causes thepressure plate 8 to descend and to press the web 7 against the upperside of the gate 6. As the pressure plate 8 moves toward the gate 6, theleaf spring 23 undergoes deformation as soon as the pad 23a begins tobear against the rear side of the web 7 opposite the back support 24.The upper surface of the back support 24 is preferably smooth so that itoffers negligible resistance to sliding movement of the web 7 in thedirection indicated by arrow A. The friction between the rear side ofthe web 7 and the pad 23a is more pronounced so that the pad 23a tendsto push the web 7 in a direction to the right to thereby tension thatportion of the web which extends between the advancing rolls 15, 16 andthe back support 24. The peripheral surfaces of the rolls 15, 16 arepreferably provided on a material having a high coefficient of frictionso that the rolls 15, 16 pinch the web 7 with a force which suffices toprevent withdrawal of web from the cassette 9 while the pressure plate 8moves toward its operative position. Furthermore, the conventionalspring or springs which bias the advancing rolls 15, 16 toward eachother are strong enough to prevent the web 7 from sliding relative tothe rolls 15, 16 during deformation of the leaf spring 23, i.e., duringmovement of the pressure plate 8 toward the operative position. Thus,the force which the pad 23a appliesto the rear side of the web 7 is usedexclusively to tension the web in the region behind the gate 6 and tothus insure that the unexposed portion of the photosensitive layer whichregisters with the window 60 is invariably located in a predeterminedplane not later than when the pressure plate 8 moves into actualclamping engagement with the rear side of the web. This insures that theweb 7 lies flat against the rear side of the gate 6 not later than whenthe pressure plate 8 reaches its operative position. The pad 23a beginsto slip along the rear side of the web 7 as soon as the latter isproperly tensioned for engagement by the pressure plate 8. The loopforming roller 17 insures that the web portion between the pad 23a andthe guide roller 18 remains under requisite tension during exposure ofphotosensitive material behind the window 6a to printing light issuingfrom the source 1 and passing through the original 4. The pressure whichthe plate 8 applies against the rear side of the web 7 suffices toprevent any shifting of the web during the making of an exposure, evenif the deformation of leaf spring 23 has reached and exceeds a stageduring which the pad 23a subjects the web to a maximum tensioningaction.

It was found that the apparatus of FIG. 1 is capable of transporting theweb with a high degree of accuracy so that the machine including theparts shown in FIG. 1 can be used for the making of customary printswith margins at two or more sides as well as for the making of so-calledmarginless prints.

Upon completion of an exposure, the pressure plate 8 is returned to theillustrated inoperative position whereby the leaf spring 23 reassumesits normal shape to lift the pad 23a off the rear side of the web 7 orto maintain the pad in negligible frictional engagement with the rearside of the web so that the latter can readily advance lengthwise inresponse to renewed rotation of the advancing rolls 15, 16 and takeupreel 21. During movement of the pressure plate 8 toward the illustratedinoperative position, the leaf spring 23 moves the pad 23a counter tothe direction indicated by arrow A; however, this need not result in anyappreciable movement of the web toward the advancing rolls 15, 16because the bias of the spring 17a can be readily selected in such a waythat the loop forming roller 17 opposes the leftward movement of the webduring lifting of the pressure plate. At any rate. the loop formingroller 17 will immediately tension or tauten the web downstream of theadvancing rolls 15, 16 not later than when the pressure plate 8 returnsto the inoperative position of FIG. 1 so that the advancing rolls 15, 16can begin with the next stepwise transport of the web 7 in order toplace the next unexposed portion of the photosensitive layer intoregister with the window 6a. The pressure plate 8 thereupon descends andthe pad 23a tensions the web 7 prior to making of the next exposure.

The leaf spring 23 can be said to constitute a onepiece springy couplingbetween the soft rubber pad 23a and the bracket 8a of the pressure plate8. FIG. 2 illustrates a modified coupling which constitutes a simplelinkage and includes a plate-like shoe 25 for a softrubber frictiongenerating pad 25a. The linkage movably connects the pad 250 to thepressure plate 8 in such a way that the pad 25a automatically moves inthe direction indicated by arrow A when the pressure plate 8 is causedto move toward its operative position. The shoe 25 is articulatelyconnected to a shank or stem 25b and is biased downwardly by a helicalspring 26 which insures that the pad 25a is located close to or evenabuts against the rear side of the web 7 while the pressure plate 8dwells in the illustrated inoperative position. The upper end portion ofthe shank 25b is reciprocable in and can swivel relative to an aperturedlug 28 provided on a carrier or frame 29 which is secured to or forms anintegral part of the pressure plate 8. The carrier 29 is furtherprovided with an inclined arcuate guide slot 29a for a pin 27 which issecured to the shank 25b or directly to the shoe 25.

When the pressure plate 8 moves toward the gate 6, the spring 26 isdeformed and the pad 25a is caused to move in the direction indicated byarrow A because the shank 25b slides in the lug 28 whereby. the pin 27slides in the inclined slot 29a to thus compel the shoe 25 to move awayfrom the window 6a and away from the advancing rolls (not shown). Thisresults in a tensioning of that portion of the web 7 which extendsbetween the advancing rolls and the pad 25a. Since the shoe 25 isarticulately connected with the shank 25b, the plane of the pad 25aremains at least substantially parallel to the plane of the web 7 whilethe pad 25 moves in the direction indicated by the arrow A. The mannerin which the web 7 is stored upstream and downstream of the window 6a ispreferably the same as or analogous to that shown in FIG. 1.

A further coupling between the pressure plate 8 and a frictiongenerating pad 32a of soft rubber is shown in FIG. 3. This couplingcomprises a lever 30 which is pivoted to the pressure plate 8, as at30a, and carries a pivotable shoe 32 for the pad 32a. A stop pin 31 onthe pressure plate 8 serves as an abutment for the lever 30 so that thelatter normally assumes the illustrated in clined position when thepressure plate 8 is caused to assume the inoperative or retractedposition shown in FIG. 3. The back support 24 is shown as forming anintegral plate-like part of the gate 6; however, it is clear that theback support 24 of FIG. 1, 2 or 3 can constitute a discrete part whichneed not even be fixed to the gate 6.

When the pressure plate 8 is retracted, the lever 30 pivots by gravityand abuts against the stop pin 31 to thereby maintain the pad 32a out ofengagement with or close to the rear side of the web 7. When theactuating mechanism (e.g., an electromagnet) causes the pressure plate 8to move toward its operative position, the lever 30 is automaticallycompelled to pivot in the direction indicated by arrow A (i.e., awayfrom the advancing rolls and the window 6a) whereby the pad 32a tensionsthe web 7 between the advancing rolls and the back support 24. The pad32a slides relative to the rear side of the web 7, at least during thelast stage of movement of the pressure plate 8 toward its operativeposition. The friction between the preferably smooth upper surface ofthe back support 24 and the front side of the web 7 is much less thanthe friction between the pad 32a and the rear side of the web.

FIG. 4 illustrates a further web transporting apparatus wherein the gate6 supports pairs of guide pins 49a, 50a and pairs of helical springs 49,50 for a reciprocable pressure plate 108. The springs 49, 50 permanentlyurge the pressure plate 108 to the illustrated inoperative or retractedposition. The advancing rolls 15, 16 are located downstream or behindthe window 60, as viewed in the direction (arrow A) of stepwise movementof the web 7. The gate 6 comprises an integral ex tension or backsupport 24 located opposite a substantially U-shaped rubber-coatedfriction generating device 123a provided on an elastic displacing memberor holder 123 pivotably mounted in the frame of the printing machine, asat 123b. That portion of the pressure plate 108 which overlies the backsupport 24 is provided with an opening 108b through which the frictiongenerating device 123a extends to engage the rear side of the web 7 whenthe displacing member or holder 123 is caused to pivot in acounterclockwise direction, as

, viewed in FIG. 4. The actuating means for the displacing member 123includes a rotary electromagnet 48 having an armature 48a which isrotated counterclockwise, as viewed in FIG. 4, when the electromagnet 48is energized, whereby the friction generating device 123a bears againstthe web 7 above the back support 24 and simultaneously moves counter tothe direction indicated by arrow A in response to deformation of thedisplacing member 123. A spring 123C or the like serves to maintain thedisplacing member 123 in constant engagement with the roller-shaped endportion 48b of the armature 48a. The end portion 4812 additionallyserves to engage a projection 108a of the pressure plate 108 and to movethe pressure plate to the operative position against the opposition ofsprings 49, 50 when the electromagnet 48 rotates its armature 48a in acounterclockwise direction.

The pressure plate 108 can be provided with suitable rails, walls oranalogous confining means which serve to prevent lateral movements ofthe web 7 so that the web is held for lengthwise movement along anaccurately determined path. The aforementioned confining means can entersuitable recesses of the gate 6 when the pressure plate 108 descends inresponse to energization of the electromagnet 48.

When the electromagnet 48 is deenergized, the spring 1236 moves thedisplacing member 123 to the illustrated position whereby the displacingmember holds the friction generating device 123a in a starting positionof disengagement from the rear side of the web 7. The path for the web 7above the gate 6 is then totally unobstructed so that the leader of afresh web can be readily introduced into the nip of the advancing rolls15, 16.

The electromagnet 48 is energized upon completed lengthwise transport ofthe web 7 through a distance which is required to place a freshincrement of the photosensitive layer at the underside of the web intoregister with the window 6a. The energization of electromagnet 48entails a counterclockwise movement of the armature 48a whereby the endportion 48b pivots the displacing member 123 against the opposition ofthe spring 1236 and causes the friction generating device 123a to bearagainst the web 7 opposite the back support 24. As the armature 48acontinues to pivot, the point of contact between the device 123a and theweb 7 moves counter to the direction indicated by arrow A (i.e., awayfrom the window 6a and advancing rolls 15, 16) to subject the webportion between the advancing rolls and the back support 24 to requisitetension. The movement of friction generating device 123a counter to thedirection indicated by arrow A may coincide with or may precede theengagement of the end portion 48b with the projection 108a. Thus, themovement of the pressure plate 108 to its operative position ofengagement with the rear side of the web 7 may take place simultaneouslywith or may follow the tensioning action of the friction generatingdevice 123a. Such tensioning action is completed not later than when thepressure plate 108 begins to bear against the rear side of the web 7.

Upon completion of an exposure, the electromagnet 48 is deenergizedwhereby the spring 123c returns the parts 48a, 48b, 123 and 123a to theillustrated positions. At the same time, the springs 49, 50 return thepressure plate 108 to the illustrated inoperative position. Theadvancing rolls 15, 16 are thereupon driven through a predeterminedangle to place a fresh increment of photosensitive layer on the web 7into register with the window 60.

It is clear that the electromagnet 48 may be energized to move thearmature 48a back to the illustrated position; the apparatus is thenprovided with a spring which is strong enough to cause the frictiongenerating device 123a to tension the web 7 in response todeenergization of the electromagnet. Thus, the electromagnet 48 assumesa first (energized or deenergized) condition to effect a movement of thedevice 123a toward the back support 24 and away from the window 6a, anda second (deenergized or energized) condition to effect a movement ofthe device 123a back to the starting position. It is also clear that theelectromagnet 48 constitutes but one form of actuating means which canbe used to cause the displacing member 123 to move the frictiongenerating device relative to the back support 24. For example, theelectromagnet 48 can be replaced by a motor, such as an electric motor.It is equally within the purview of the invention to provide firstactuating means for displacing member 123 and discrete second actuatingmeans for moving the pressure plate 108 to its operative position.

FIG. 5 illustrates a portion of a further apparatus wherein thedisplacing means for the friction generating device 34a (e.g., asoft-rubber pad) constitutes a rotary electromagnet 33 having apivotable armature or lever 34. The web is shown at 7, the gate at 6,the window at 6a and the back support at 24. The advancing rolls (notshown) are assumed to be located upstream (to the left) of the window 6aso as to intermittently advance the web 7 in the direction indicated byarrow A. The electromagnet 33 includes a return spring (not shown) whichurges the armature 34 in a clockwise direction, as viewed in FIG. 5, sothat, when the electromagnet 33 is deenergized, the armature 34 abutsagainst a stop pin 34a to maintain the friction generating device 34a inthe starting position which is indicated by solid lines. The center ofcurvature of the arcuate friction generating device 34a is preferablylocated on or close to the pivot axis of the armature 34.

When the electromagnet 33 is energized, the armature 34 turns in acounterclockwise direction, as viewed in FIG. 5, and moves the frictiongenerating device 34a to the position indicated by broken lines. Duringsuch movement, the device 340 moves into progressively strongerfrictional engagement with the rear side of the web 7 and tensions theweb between the advancing rolls and the back support 24 so that the webis properly tensioned not later than when its rear side is engaged bythe pressure plate, not shown.

The circuit of the electromagnet 33 is illustrated in FIG. 6. A shaft133 which drives the advancing rolls also drives a cam 134 whichcompletes a full revolution during a complete cycle including thelengthwise transport of web 7 by a step, the energization ofelectromagnet 33, the movement of pressure plate to its operativeposition, and deenergization of the electromagnet. The circuit comprisesa control switch 35 which is normally closed and can be opened by a lobeof the cam 134 when the shaft 133 begins to rotate the advancing rolls.The switch 35 is in series with the winding of the electromagnet 33 andwith a normally open control switch 36 which is connected in parallelwith a switch 37 in the holding circuit of the electromagnet. Thecontrol switch 36 is closed for a short interval of time by a secondlobe of the cam 134 (or by a lobe of a second cam, not shown) uponcompleted stepwise transport of the web 7.

When the shaft 133 has caused the advancing rolls to transport the web 7of FIG. by a step so as to place a fresh increment of the photosensitivelayer into register with the window 6a, the cam 134 closes the controlswitch 36 for a short interval of time to energize the electromagnet 33which moves the armature 34 to the broken-line position of FIG. 5 sothat the friction generating device 34a tensions the web 7 by tending tomove the web in the direction indicated by arrow A. The pressure platethereupon descends to assume its operative position and to press the web7 against the rear side of the gate 6. The electromagnet 33 closes theswitch 37 when the armature 34 reaches the brokenline position of FIG. 5whereby the circuit of the electromagnet remains completed regardless ofthe position of the control switch 36. Thus, the armature 34 maintainsthe friction generating device 34a in the broken-line position of FIG. 5during the making of an exposure. The shaft 133 continues to rotate andcauses the cam 134 to open the control switch 35 for a short interval oftime upon completion of an exposure to thus deenergize the electromagnet33 whereby the aforementioned spring returns the armature 34 and thefriction generating device 34a to the solid-line positions of FIG. 5.The pressure plate then returns to its inoperative position and theshaft 133 again causes the advancing rolls to transport the web 7 by astep while the electromagnet 33 remains deenergized. The switch 37 opensas soon as the armature 34 leaves the broken-line position of FIG. 5.

FIG. 7 illustrates a modification of the apparatus shown in FIG. 5. Thefriction generating device 38 is a roller which consists of or comprisesa peripheral layer of soft rubber and is non-rotatably secured to a leafspring 39 mounted on the armature 34 of the rotary electromagnet 33. Theapparatus of FIG. 7 preferably further comprises means for adjusting theinitial stressing of the leaf spring 39 to thereby regulate the forcewith which the roller 38 tensions the web 7 when the electromagnet 33 isenergized to turn the armature 34 and the spring 39 in acounterclockwise direction. A]- ternatively, the leaf spring 39 can bereplaced by a weaker or stronger leaf spring. Another advantage of theleaf spring 39 is that it enables the roller 38 to subject the entireadjacent portion of the rear side of the web 7 to a uniform tensioningforce when the electromagnet 33 is energized. Such force reaches amaximum value shortly after the armature 34 leaves the solid-lineposition of FIG. 7 which is desirable because the adjacent portion ofthe web 7 is thereby subjected to a maximum acceleration in a direction(arrow A) away from the advancing rolls (not shown and assumed to belocated to the left of the window 6a). The extent of counterclockwisepivotal movement of the armature 34 is preferably selected in such a waythat the roller 38 moves beyond a dead-center position in which theadjacent portion of the web 7 is subjected to a maximum tensioningstress. This allows for a reduction of the force with which theelectromagnet 33 must maintain the roller 38 in the broken-line secondposition of FIG. 7.

A further advantage of the leaf spring 39 is that it can compensate foreventual inaccuracies in selection of the distance between the pivotaxis of the armature 34 and the back support 24 and for varyingthicknesses of 5 successive webs. The circuit of the electromagnet 33 ofFIG. 7 is preferably identical with or similar to the circuit of FIG. 6.

Referring to FIG. 8, there is shown an apparatus wherein the frictiongenerating device is a cylindrical 1O sleeve or roller 41 consisting ofsoft rubber and secured for rotation to a core 40 rigid with a shaft 400which carries a gear 42 in mesh with a driver gear 43. The latter isdriven by the output shaft of an electric motor 44 (see FIG. 9). Theperiphery of the sleeve 41 is provided with three equidistant recessesor flats 410 which alternate with convex web-engaging portions 41b. Inthe illustrated embodiment, the sleeve 41 has three recesses 41a andthree convex portions 41b. The distance between the axis of the shaft400 and the back support 24 is selected in such a way that the convexportions 41b of the sleeve 41 can engage and tension the web 7 when thecore 40 is rotated in a counterclockwise direction, as viewed in FIG. 8,so as to place a convex portion 41b into engagement with the rear sideof the web 7. The

direction in which the web 7 is transported by the advancing rolls (notshown) is indicated by the arrow A. The advancing rolls are located tothe left of the window 6a.

The number of teeth on the gear 42 is six times the number of teeth onthe driver gear 43. Thus, when the motor 44 rotates the gear 43 through360, the sleeve 41 turns through 60 so as to move a recess 41a or thenext-following convex portion 41b into register with the back support24.

The output shaft of the motor 44 further carries a disk-shaped cam 45having a lobe 45a which can open a normally closed control switch 46connected in series with the motor 44 and in parallel with a starterswitch 47. The starter switch 47 is normally open and is closed for ashort interval of time upon completion and also prior to completion ofeach stepwise transport of the web 7. The lobe a maintains the switch 46in open position when the motor 44 is idle.

The operation of the apparatus of FIGS. 8 and 9 is as follows:

The sleeve 41 assumes the angular position of FIG. 8 prior to start ofstepwise transport of the web 7 by the advancing rolls. Since thelowermost recess 41a of FIG.

8 is adjacent to the smooth upper surface of the back support 24, theadvancing rolls can transport the web 7 without any interference on thepart of the sleeve 41. When the transport of the web 7 is completed, thestarter switch 47 is closed (for example, by one of the advancing rollsin a manner not shown in FIG. 9) to thus complete the circuit of themotor 44. The motor rotates the cam 45 so that the lobe 450 allows theswitch 46 to close whereby the switch 46 completes the motor circuitirrespective of the position of the starter switch 47. The motor 44 alsorotates the driver gear 43 which rotates the gear 42 and hence thesleeve 41 so that the latter moves the lowermost recess 41a away fromthe back support 24 and causes the next-following convex portion 41b toengage and tension the web 7 prior to movement of the pressure plate(not shown) to its operative position. The lobe 45a again opens theswitch 46 to arrest the motor 44 after the gear 43 completes a fullrevolution and thus causes the gear 42 to turn the sleeve 41 through 60.Eventual inaccuracies in the extent of angular displacement of the gear42 are compensated for by slippage of the sleeve 41 relative to the rearside of the web 7.

The starter switch 47 is closed again upon completion of an exposurewhereby the motor 44 is started and causes the sleeve 41 to turn through60 so as to move the next recess 41a opposite the back support 24. Thisinsures that, when the advancing rolls are set in motion, the web 7 canmove lengthwise (arrow A) without any interference on the part of thesleeve 41.

It will be seen that the advancing rolls 15, 16 can be located ahead ofor behind the friction generating device (compare, for example, theFIGS. 1 and 4). It is further clear that the rigid plate-like stationaryback support 24 can be replaced by a back support in the form of anidler roller which is rotated by the friction generating device throughthe intermediary of the web while the friction generating device movesin a direction away from the advancing rolls. Still further, and asalready mentioned before, the electromagnet 48 or 33 can be energized toeffect a movement of the friction generating device to or from itsstarting position.

If the friction generating device is spaced apart from the web when theadvancing rolls are set in motion (see FIG. 5 or 8), the actuating meansfor the displacing means can be started before the transport of the webby the advancing rolls is completed, i.e., the sleeve or roller 41 ofFIG. 8 can begin to rotate even before the advancing rolls are arrested.This reduces the overall time which is spent for the making of anexposure because the sleeve 41 can engage and tension the web 7 as soonas the advancing rolls come to a halt. When the friction generatingdevice is in continuous contact with the rear side of the web (e.g., asshown in FIG. 1), the actuating means for the displacing means ispreferably started after the advancing rolls come to a standstill. It isclear, however, that the displacing means can begin to move the frictiongenerating device away from the advancing rolls even before theadvancing rolls come to a standstill, even if the friction generatingdevice is in continuous engagement with the web. Referring again to FIG.1, and assuming that the pressure plate 8 begins to descend before theadvancing rolls l5, 16 are arrested, the friction generating device 23awill assist the advancing rolls 15, 16 in moving the web 7 in thedirection indicated by arrow A as long as the advancing rolls rotate andthereupon begins to tension the web to complete the tensioningstepbefore the pressure plate 8 reaches its operative position.

At the present time, we prefer to place the advancing rolls 15, 16upstream of the window 6a because the ad vancing rolls then also serveas a means for threading the web through the printing machine.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. Apparatus for stepwise transport of elongated webs, particularly forstepwise transport of photosensitive webs in photographic printing orcopying machines, comprising a pair of intermittently driven advancingrolls arranged to transport a web lengthwise along a predetermined path;a friction generating device adjacent to one side of said path and beingspaced apart from said advancing rolls; a back support adjacent to theother side of said path opposite said friction generating device; a gateadjacent to said other side of said path and located between saidadvancing rolls and said friction generating device; and displacingmeans actuatable to urge said friction generating device toward saidback support and to simultaneously move said friction generating deviceaway from said advancing rolls whereby said friction generating devicetensions the web between said advancing rolls and said back support,said displacing means comprising a pressure plate located at said oneside of said path opposite said gate and being movable between aninoperative position away from and an operative position of engagementwith the web portion between said pressure plate and said gate, andcoupling means movably connecting said pressure plate with said frictiongenerating device so that the latter moves away from said advancingrolls in response to movement of said pressure plate to said operativeposition.

2. Apparatus as defined in claim 1, said gate has a window and saidadvancing rolls are operable to transport successive increments of theweb into register with said window.

3. Apparatus as defined in claim 1, wherein said back support has asurface which is engaged by the web in response to actuation of saiddisplacing means, the friction between the web and said surface duringmovement of said friction generating device away from said advancingrolls being less than the friction between the web and said device sothat the web tends to share the movement of said device away from saidadvancing rolls.

4. Apparatus as defined in claim 1, further comprising means foractuating said displacing means upon completion of each intermittentmovement of said advancing rolls.

5. Apparatus as defined in claim 1, further comprising means forstarting the actuation of said displacing means during the last stage ofeach intermittent move ment of said advancing rolls.

6. Apparatus as defined in claim 1, wherein said friction generatingdevice is located behind said advancing rolls, as considered in thedirection of movement of the web along said path.

7. Apparatus as defined in claim 1, wherein said back support comprisesa rigid plate-like member.

8. Apparatus as defined in claim 1, wherein said coupling meanscomprises a spring.

9. Apparatus as defined in claim 1, wherein said coupling meanscomprises a linkage supported by said pressure plate.

10. Apparatus as defined in claim 1, wherein said coupling meanscomprises a lever pivotably secured to said pressure plate.

11. Apparatus for stepwise transport of elongated webs, particularly forstepwise transport of photosensitive webs in photographic printing orcopying machines, comprising a pair of intermittently driven advancingrolls arranged to transport a web lengthwise along a predetermined path;a friction generating device adjacent to one side of said path and beingspaced apart from said advancing rolls; a back support adjacent to theother side of said path opposite said friction generating device; a gateadjacent to said other side of said path and located between saidadvancing rolls and said friction generating device; a pressure plateadjacent to said one side of said path opposite said gate, said pressureplate having an opening and being movable between an inoperativeposition spaced apart from and an operative position of engagement withthe web portion between said advancing rolls and said frictiongenerating device; and displacing means actuatable to urge said frictiongenerating device toward said back support and to simultaneously movesaid friction generating device away from said advancing rolls wherebysaid friction generating device tensions the web between said advancingrolls and said back support, sai ddisplacing means comprising a holderfor said friction generating device and said holder being movablethrough said opening of said pressure plate to move said device intoengagement with the web in response to actuation of said displacingmeans.

12. Apparatus as defined in claim 11, further comprising actuating meansfor said displacing means, said actuating means including means formoving said pressure plate to said operative position in response tomovement of said friction generating device away from said advancingrolls.

13. Apparatus for stepwise transport of elongated webs, particularly forstepwise transport of photosensitive webs in photographic printing orcopying machines, comprising a pair of intermittently driven advancingrolls arranged to transport a web lengthwise along a predetermined path;a friction generating device adjacent to one side of said path and beingspaced apart from said advancing rolls; a back support adjacent to theother side of said path opposite said friction generating device;displacing means actuatable to urge said friction generating devicetoward said back support and to simultaneously move said frictiongenerating device away from said advancing rolls whereby said frictiongenerating device tensions the web between said advancing rolls and saidback support, said displacing means comprising electromagnet meansincluding an armature and having an energized condition and adeenergized condition, said friction generating device being mounted onsaid armature; first control means for causing said electromagnet meansto assume one of said conditions upon completion of intermittentmovement of said advancing rolls whereby said armature moves saidfriction generating device from a starting position toward a secondposition to thereby tension the web; and second control means forcausing said electromagnet means to assume the other of said conditionsprior to renewed start of intermittent movement of said advancing rollswhereby said armature returns said friction generating device to saidstarting position.

14. Apparatus as defined in claim 13, wherein said electromagnet meanscomprises a rotary electromagnet and said armature includes a leverwhich is pivotable in response to a change in the condition of saidelectromagnet means to thereby move said friction generating device in adirection away from said advancing rolls.

15. Apparatus for stepwise transport of elongated webs, particularly forstepwise transport of photosensitive webs in photographic printing orcopying machines, comprising a pair of intermittently driven advancingrolls arranged to transport a web lengthwise along a predetermined path;a friction generating device adjacent to one side of said path and beingspaced apart from said advancing rolls; a back support adjacent to theother side of said path opposite said friction generating device;displacing means actuatable to urge said friction generating devicetoward said back support and to simultaneously move said frictiongenerating device away from said advancing rolls whereby said frictiongenerating'device tensions the web between said advancing rolls and saidback support, said displacing means comprising electromagnet meansincluding an armature, said friction generating device being mounted onsaid armature and said displacing means further comprising resilientmeans connecting said friction generating device to said armature, saidfriction generating device being movable beyond a dead-center positionin response to completed actuation of said displacing means to move saidfriction generating device away from said advancing rolls.

16. Apparatus as defined in claim 15, wherein said resilient meanscomprises a leaf spring.

17. Apparatus for stepwise transport of elongated webs, particularly forstepwise transport of photosensitive webs in photographic printing orcopying machines, comprising a pair of intermittently driven advancingrolls arranged to transport a web lengthwise along a predetermined path;a friction generating device adjacent to one side of said path and beingspaced apart from said advancing rolls, said friction generating devicecomprising a roller which is rotatable about its axis and consists atleast in part of a material having a high coefficient of friction, saidroller having at least one recessed portion and at least one secondportion; a back support adjacent to the other side of said path oppositesaid friction generating device; and displacing means actuatable to urgesaid friction generating device toward said back support and tosimultaneously move said friction generating device away from saidadvancing rolls whereby said friction generating device tensions the webbetween said advancing rolls and said back support, said displacingmeans comprising means for rotating said roller of said frictiongenerating device between a first position in which said recessedportion of said roller is adjacent to said back support so that saidroller is at least substantially disengaged from the web in said pathand a second position in which the web is engaged by said second portionof said roller whereby said second portion of said roller tends to movethe web away from said advancing rolls in response to continued rotationof said roller.

1. Apparatus for stepwise transport of elongated webs, particularly forstepwise transport of photosensitive webs in photographic printing orcopying machines, comprising a pair of intermittently driven advancingrolls arranged to transport a web lengthwise along a predetermined path;a friction generating device adjacent to one side of said path and beingspaced apart from said advancing rolls; a back support adjacent to theother side of said path opposite said friction generating device; a gateadjacent to said other side of said path and located between saidadvancing rolls and said friction generating device; and displacingmeans actuatable to urge said friction generating device toward saidback support and to simultaneously move said friction generating deviceaway from said advancing rolls whereby said friction generating devicetensions the web between said advancing rolls and said back support,said displacing means comprising a pressure plate located at said oneside of said path opposite said gate and being movable between aninoperative position away from and an operative position of engagementwith the web portion between said pressure plate and said gate, andcoupling means movably connecting said pressure plate with said frictiongenerating device so that the latter moves away from said advancingrolls in response to movement of said pressure plate to said operativeposition.
 2. Apparatus as defined in claim 1, said gate has a window andsaid advancing rolls are operable to transport successive increments ofthe web into register with said window.
 3. Apparatus as defined in claim1, wherein said back support has a surface which is engaged by the webin response to actuation of said displacing means, the friction betweenthe web and said surface during movement of said friction generatingdevice away from said advancing rolls being less than the frictionbetween the web and said device so that the web tends to share themovement of said device away from said advancing rolls.
 4. Apparatus asdefined in claim 1, further comprising means for actuating saiddisplacing means upon completion of each intermittent movement of saidadvancing rolls.
 5. Apparatus as defined in claim 1, further comprisingmeans for starting the actuation of said displacing means during thelast stage of each intermittent movement of said advancing rolls. 6.Apparatus as defined in claim 1, wherein said friction generating deviceis located behind said advancing rolls, as considered in the directionof movement of the web along said path.
 7. Apparatus as defined in claim1, wherein said back support comprises a rigid plate-like member. 8.Apparatus as defined in claim 1, wherein said coupling means comprises aspring.
 9. Apparatus as defined in claim 1, wherein said coupling meanscomprises a linkage supported by said pressure plate.
 10. Apparatus asdefined in claim 1, wherein said coupling means comprises a leverpivotably secured to said pressure plate.
 11. Apparatus for stepwisetransport of elongated webs, particularly for stepwise transport ofphotosensitive webs in photographic printing or copying machines,comprising a pair of intermittently driven advancing rolls arranged totransport a web lengthwise along a predetermined path; a frictiongenerating device adjacent to one side of said path and being spacedapart from said advancing rolls; a back support adjacent to the otherside of said path opposite said friction generating device; a gateadjacent to said other side of said path and located between saidadvancing rolls and said friction generating device; a pressure plateadjacent to said one side of said path opposite said gate, said pressureplate having an opening and being movable between an inoperativeposition spaced apart from and an operative position of engagement withthe web portion between said advancing rolls and said frictiongenerating device; and displacing means actuatable to urge said frictiongEnerating device toward said back support and to simultaneously movesaid friction generating device away from said advancing rolls wherebysaid friction generating device tensions the web between said advancingrolls and said back support, sai ddisplacing means comprising a holderfor said friction generating device and said holder being movablethrough said opening of said pressure plate to move said device intoengagement with the web in response to actuation of said displacingmeans.
 12. Apparatus as defined in claim 11, further comprisingactuating means for said displacing means, said actuating meansincluding means for moving said pressure plate to said operativeposition in response to movement of said friction generating device awayfrom said advancing rolls.
 13. Apparatus for stepwise transport ofelongated webs, particularly for stepwise transport of photosensitivewebs in photographic printing or copying machines, comprising a pair ofintermittently driven advancing rolls arranged to transport a weblengthwise along a predetermined path; a friction generating deviceadjacent to one side of said path and being spaced apart from saidadvancing rolls; a back support adjacent to the other side of said pathopposite said friction generating device; displacing means actuatable tourge said friction generating device toward said back support and tosimultaneously move said friction generating device away from saidadvancing rolls whereby said friction generating device tensions the webbetween said advancing rolls and said back support, said displacingmeans comprising electromagnet means including an armature and having anenergized condition and a deenergized condition, said frictiongenerating device being mounted on said armature; first control meansfor causing said electromagnet means to assume one of said conditionsupon completion of intermittent movement of said advancing rolls wherebysaid armature moves said friction generating device from a startingposition toward a second position to thereby tension the web; and secondcontrol means for causing said electromagnet means to assume the otherof said conditions prior to renewed start of intermittent movement ofsaid advancing rolls whereby said armature returns said frictiongenerating device to said starting position.
 14. Apparatus as defined inclaim 13, wherein said electromagnet means comprises a rotaryelectromagnet and said armature includes a lever which is pivotable inresponse to a change in the condition of said electromagnet means tothereby move said friction generating device in a direction away fromsaid advancing rolls.
 15. Apparatus for stepwise transport of elongatedwebs, particularly for stepwise transport of photosensitive webs inphotographic printing or copying machines, comprising a pair ofintermittently driven advancing rolls arranged to transport a weblengthwise along a predetermined path; a friction generating deviceadjacent to one side of said path and being spaced apart from saidadvancing rolls; a back support adjacent to the other side of said pathopposite said friction generating device; displacing means actuatable tourge said friction generating device toward said back support and tosimultaneously move said friction generating device away from saidadvancing rolls whereby said friction generating device tensions the webbetween said advancing rolls and said back support, said displacingmeans comprising electromagnet means including an armature, saidfriction generating device being mounted on said armature and saiddisplacing means further comprising resilient means connecting saidfriction generating device to said armature, said friction generatingdevice being movable beyond a dead-center position in response tocompleted actuation of said displacing means to move said frictiongenerating device away from said advancing rolls.
 16. Apparatus asdefined in claim 15, wherein said resilient means comprises a leafspring.
 17. Apparatus for stepwise transport of elongated webs,particularly for stepwise transport of photosensitive webs inphotographic printing or copying machines, comprising a pair ofintermittently driven advancing rolls arranged to transport a weblengthwise along a predetermined path; a friction generating deviceadjacent to one side of said path and being spaced apart from saidadvancing rolls, said friction generating device comprising a rollerwhich is rotatable about its axis and consists at least in part of amaterial having a high coefficient of friction, said roller having atleast one recessed portion and at least one second portion; a backsupport adjacent to the other side of said path opposite said frictiongenerating device; and displacing means actuatable to urge said frictiongenerating device toward said back support and to simultaneously movesaid friction generating device away from said advancing rolls wherebysaid friction generating device tensions the web between said advancingrolls and said back support, said displacing means comprising means forrotating said roller of said friction generating device between a firstposition in which said recessed portion of said roller is adjacent tosaid back support so that said roller is at least substantiallydisengaged from the web in said path and a second position in which theweb is engaged by said second portion of said roller whereby said secondportion of said roller tends to move the web away from said advancingrolls in response to continued rotation of said roller.